What's the difference with regards to annexing or not annexing?

You storm into a country, you kill a lot of people, repeatedly, you do not care about these people in the slightest, you bomb weddings for a decade, you put up whatever government that you want there. But at least you did not annex the country, i.e. did not take responsibility for it and its citizens.

It is also "not a genocide", say you.

It's a totally different thing.